Abstract: An apparatus includes a source configured to generate a beam of electromagnetic radiation propagating in a first direction and a spatial filter. The spatial filter is configured to restrict the beam of electromagnetic radiation in one or more dimensions and includes at least one set of rods including a first rod and a second rod. The first rod is a first cylindrical structure with a first axis in a first plane and the second rod is a second cylindrical structure with a second axis in a second plane parallel to the first plane. The first axis and the second axis are longitudinal axes, and the first and the second rods have shaped surfaces in portions of their respective surfaces facing one another.

Abstract: A laser beam is utilized to ignite the fuel and oxidizer injected into a combustion chamber. An injector has a plurality of injector elements each injecting fuel and oxidizer into a flame holding zone adjacent the injector face plate where fuel and oxidizer are mixing at a rate to sustain flammability. The laser beam is introduced parallel to the injector face plate passing through the fuel and oxidizer mixing zones igniting the propellants. The propellants are ignited by having a laser beam tuned to a frequency to excite the oxidizer such that it will chemically combine with the fuel to form an ignition kernel in the flame holding zone. When a plurality of injector elements are ignited in this manner a controlled ignition process in the combustion chamber is achieved.

Abstract: A photon-counting spatial light modulator that has an avalanche photodiode structure and is designed to operate in Geiger mode is sensitive to a single photon of light. An avalanche photodiode having an applied electric field is excited by an optical wave comprising one or more photons whose energies exceed the band-gap energy of the photodiode material. This localized electrical excitation alters the refractive index of the material through various effects, most notably the transient thermo-optic effect and the photorefractive effect. A second optical wave is incident during or shortly after the electrical excitation, and comprises photons whose energy is less than or nearly equal to the band-gap energy. This second optical wave is then used to read out the avalanche-induced variation in refractive index.